I ran a predator, shaman and sorcerer up to levels 11, 14 and 12 respectively during beta. I spent most but not all of my time solo . Each class was a lot of fun to play solo and with a group. You can have a lot of sucess solo if you learn how to use your heroic option wheel (HO for short). SOE has changed how it works during the beta a few times and this is based on how it was working on Nov 6.
You can invoke the HO wheel by using a 0 cost, 0 casting time spell. I would typically initiate combat with an attack or spell, hit the HO button and then try to finish up a combo and try it again. Depending on which option the wheel generated, you could get an attack or spell landing 2x-3x damage in addition to the normal spell. This extra DPS is huge at the early levels and makes all the difference when you are solo. The HO works in a groups too but everyone must work together to make it work. It takes a bit of practice.
During the beta, most people thought the classes that could heal themselves were better for solo. I found healing class DPS to be lower than the scout and the mage and therefore they needed the healing.
While playing the predator, if I used the sneak and a got a good backstab in to start out combat, I never had any trouble with the mob. My scout was duel wielding some daggers and was hitting for 7-12 points during normal combat, around 20 on some special moves, but my best backstab would hit for 70+ to start out combat and it hit for 89 points one time. You _really_ don't want the predator class getting behind you.
For my sorcerer, I skipped the mage/pet route and went with pure offense. My Euridite had plenty of mana so I took the stamina option whenever I had a choice because the hit points don't last as long as the mana. Now this class was able to deal with groups of two by rooting one (and only rooting it) and attacking the other mob. In my experience, the root never broke before expiration unless the mobs was damaged. At level 12, I received a choice of specializing against gnoll or orcs. Since I was in Qeynos, I took gnolls and I received an anti-gnoll spell. When i was able to use it as part of the HO cycle, it crashed into the gnoll for 105 points. Needless to say, I was very pleased and the gnoll shaman was very dead.
Summary.
All three classes solo well. For me, the mage-->sorcerer route leveled up the quickest, followed by the predator and then the shaman. HOWEVER, my shaman could solo the tougher mobs than either the predator or sorcerer but the downtime wasn't worth it. As far as I could tell, the classes were very well balanced. Try them out, enjoy it, don't worry about finding a solution yet, there isn't one so have fun.